Hey It's awesome that you've starting training. I started training when I was 39. I'm 42 now and I'm so glad I didn't let the early white belt discouragements force me to quit. My kicks are still not as high as I like. The thing I notice is that I was looking at Martial Artist in training with me that have been doing this for a long time. I would watch them which is good to learn, but I forgot to watch myself train. So during meditation at the start of class I remind myself to focus and make this time my training time and watch myself as best I can. The other thing I did was to find someone else in my class that was close to my age and ability, it helps to have a workout partner also in his forties.
Watch for your own uniqueness.
stephanos